VATMARG13100 - Specific circumstances: Apportionment of bulk purchases and sales
If a business buys eligible goods in bulk and does not intend to resell them as one lot, the price paid must be apportioned between each article. It is likely that apportionment would be used on certain global accounting transactions.
Although there is no set way of apportioning prices, the method used should be fair and reasonable; and prices allocated to each item must be as accurate as possible.
Valuation manual (VATVAL) covers apportionment in detail.